The present invention relates to microencapsulated adhesives and processes for producing such microencapsulated adhesives. More particularly, the invention relates to a process for microencapsulating solvent-based adhesives to produce an adhesive composition that is initially non-tacky but exhibits tacky properties upon application of external forces, such as shearing.
Adhesive compositions are generally tacky and gluey. However, there are numerous applications where it would be beneficial to mask the tacky nature of the adhesive prior to its use. Examples of such applications include adhesive materials for stamps or envelopes.
One potential way of rendering adhesives non-tacky is to microencapsulate the adhesive. Various attempts have been made to encapsulate adhesives such as hot melt ethylene/vinyl acetate copolymers and styrene/isoprene/styrene-type block copolymers. However, due to their high molecular weight and high viscosity, these copolymers tend to be solids at room temperature and precipitate when emulsified, and thus are very difficult to microencapsulate.
It is an object of the present invention to produce an adhesive composition that is initially non-tacky but can be made tacky when desired.
Another object of the present invention is to provide an adhesive composition that can be microencapsulated.
Another object of the present invention is to provide a solvent-based adhesive that is capable of being microencapsulated.
A further object of the present invention is to provide a microcapsule that is sufficiently porous to allow solvent to diffuse through its walls.
The present inventor has found that solvent-based adhesive compositions can be microencapsulated by well-known microencapsulation techniques, and then the solvent in these compositions can be removed from the microcapsules by means such as heating or reduced pressure. These microencapsulated adhesives are initially non-tacky, but when external forces such as shearing are applied, the microcapsules break and the tacky adhesive is exposed.